Rock physics and quantitative wavelet estimation for seismic interpretation: Tertiary North Sea

Abstract

A case study from the Tertiary of the North Sea is presented in which a well tie is improved through the application of zero offset processing and well log velocity prediction. The well ties are quantified using the techniques of White (1980, Partial coherence matching of synthetic seismograms with seismic traces. Geophysical Prospecting, 28, 333–358) and Walden & White (1984, On the errors of fit and accuracy in matching synthetic seismograms and seismic traces. Geophysical Prospecting, 32, 871–891) and log conditioning employs the Xu–White sand/clay velocity model (Xu, S. & White, R. E. 1995. A new velocity model for clay–sand mixtures. Geophysical Prospecting, 43, 91–118; Xu, S. & White, R. E. 1996. A physical model for shear-wave velocity prediction. Geophysical Prospecting, 44, 687–717). A well tie of a migrated stack section to a zero offset synthetic, produced with minimal data conditioning, gave a poor tie and event identification was in doubt. Additional data conditioning improved the tie dramatically (from 43% to 72% energy predicted and a reduction in phase error on the wavelet estimation from >20° to <10°). These enhancements in the well tie are important in justifying decisions to perform wavelet deconvolution, zero phasing or seismic trace inversion to acoustic impedance as well as correctly identifying the top reservoir reflection. This study also demonstrates that detailed log conditioning is crucial in this area to predict a diagnostic AVO (amplitude variation with offset) response related to the presence of hydrocarbons.